Destratifier for hot water tanks

ABSTRACT

A fluid flow machine consisting of a stator, mounted underneath a hot water tank, and an armature-impeller unit arranged inside said hot water tank, being separated from said stator by a spherical, magnetically permeable separation wall, which generates a toroidal vortex inside the water tank. Said vortex conveys hot water from the upper region of the tank to its lower region until the whole tank is filled with water of a uniform temperature.

BACKGROUND OF THE INVENTION

The invention is concerned with a device to produce internal circulationin hot water tanks and hot water heaters.

In large domestic hot water tanks, it is common to convey water from theupper part to the lower part of the tank by means of a circulation pump.This ensures that the cold water in the bottom part of the tank willalso be heated. In this manner, the heat content of the storage tank canbe considerably increased. The disadvantage of this method is thatconventional circulation pumps must be used. These have high electricityconsumption, have a tendency to seize, and lead to mixing of the varioustemperature zones irrespective of the temperature profile within thetank. If a large portion of the stored water is still cold, such mixingleads to an unacceptably large temperature drop in the upper zone of thetank, which feeds the hot water system.

SUMMARY OF THE INVENTION

The invention refers to a destratifier that avoids this disadvantage ofmixing the water in generating a toroidal vortex that extends verticallyupward through the storage tank. The toroidal vortex is produced by arotating impeller, which is located at the bottom of the tank. Theimpeller pushes cold water at the bottom radially outward toward thetank wall. The radially-accelerated water turns upward at the tank walland flows upward along the inside wall of the tank. At the same time,water from the top of the tank is drawn downward around the center axisto relace the upward moving cold water. Thus, the overall movement ofwater follows the shape of a toroidal vortex.

The hot water around the center axis flows from the waterbody in theupper zone downward against the buoyant forces of the hot water presentin the lower water zones. The larger the temperature difference betweenthe hot water drawn from the upper zone and the cold water lying belowit, the larger is the buoyancy of the hot water that opposes the suctiondownward. Thus, the uppermost portion will no longer participate intothe mixing process. The speed of the stream tubes of water flowingupward along the inside wall determines the amount of heat transferredto the upward moving mass of water. The increasing temperature of theupward moving water should not exceed the desired storage temperature.When the upward moving stream tubes have reached the prescribedtemperature, they become part of the upper zone of water already atfinal temperature. The interfacial front of the upper zone movesdownward until the driving motor of the impeller becomes surrounded byhot water. Then, a thermostat locted within the motor switches the motoroff, until interflowing cold water that replaces used hot water causesthe motor to switch on again.

The same destratifier can be used when hot spots in heat carryingsurfaces cause boiling in stagnant liquid. In such case, the axis of thevortex is directed toward the regions threatened by overheating.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described with the aid of the following figures:

FIG. 1 shows a hot water tank, in which a destratifier is mounted at thebottom.

FIG. 2 shows the toroidal vortex pattern in a tank nearly filled withhot water.

FIG. 3 shows the utilization of the destratifier in a gas-fired hotwater heater.

FIG. 4 shows a cross-section of a destratifier.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a hot water tank in which the water in the upper zone (1a)has already been heated by the heating jacket (2) through which the heatcarrier flows. The lower zone (1b) is still cold. The destratifier (4,5) is mounted at the center of the tank bottom (3). Its impeller (5)produces a vortex around the vertical axis (6). Hot water flows downwardalong the path of arrow (7), and is pushed by the impeller as shown byarrow (8) toward the heated inside wall of tank (1). Because of itslower density, it rises upward according to arrow (9) through the coldwater zone. In addition to the radial acceleration the impeller (5)gradually brings the entire water content of tank (1) into slowrotation. The stream tubes that are drawn downward along the path ofarrow (7) are accelerted radially outward along arrow (8) and riseaccording to arrow (9) while being heated. Thus, an interface (10) formsbetween the body of hot water in the upper zone (1a) and the cooler,lower zone (1b). The interface (10) progresses downward during heatingof the tank contents.

Without the action of the destratifier, the rate of heat transferbetween the heating jacket (2) and the lower zone (1b) decreases andapproaches zero as the body of hot water increases in depth. On theother hand, the toroidal vortex (7, 8, 9, 10) of the destratifier (4, 5)conveys cold water even from the lowest layer in the lower zone (1b). Athermostat (54) mounted within the motor (4) switches the motor offuntil new cold water enters through the inlet pipe (11). Heat transferceases only when the water also at the very bottom if the tank hasreached the prescribed storage temperature.

FIG. 2 shows the stream lines of the toroidal vortex in the hot watertank (1) in which most of the water is at the prescribed finaltemperature. Previously, in conventional systems, the mass of waterbelow plane (12) received no heat from the heating jacket (2), and therewas very little heat transfer between the zones above plane (12) and theremaining area of contact with the inside jacket surface. In contrast,the destratifier enables the entire water content of the tank to beheated. In this manner, the heat content of the fully heated tankincreases by about 50%. Because the outside surface area of the tankremains unchanged, there is no increase in heat losses to thesurroundings. Because of the decrease in surface area of the tankrequired for a given amount of heat storage, the destratifier results inenergy savings.

FIG. 3 illustrates application of the destratifier in a gas-fired hotwater heater. The combustion chamber (30) is surrounded by a jacket ofwater in the vessel (31). The flame (32) is in contact with the backwall (31') of the combustion chamber (30) in the region of the turnaround (33). The flame (32) produces such a high local temperature thatboiling occurs. The destratifier (4, 5) mounted on the back wall (31')produces a toroidal vortex (36) that causes such a high relativevelocity in region (35) that the boiling temperature is no longerachieved.

FIG. 4 shows a cross-sectional view of the destratifier according to theinvention. The motor (4) is composed of a stator comprising teeth (40),a short-circuiting yoke (41), and of coils (42). The rotating magneticfield of the stator passes through the magnetically permeable separationwall (43) and drives the pole ring (44). The pole ring (44) and theimpeller (5) form a rotating unit that is centered and supported by aball (45), which in turn forms a unit with the separation wall (43).

A ring (46) is welded to the bottom (3) of the tank. Thread bolts (47)are butt welded to the surface of the ring (46). The distance ring (48)and the collar (46') of the ring (46) form a groove for therubber-elastic O-ring (49). The counter ring (51) is pressed against therim (52) of the motor (4) by the nuts (50), which simultaneously mountthe distance ring (48) and the motor (4) to the tank.

I claim:
 1. A fluid flow machine for inhibiting thermal stratificationin a hot water tank, characterized in that an electric motor, consistingof a stator (4), with windings (40) is mounted on the outside of thebottom (3) of the tank (1) and an armature (44), supported in the centerby a ball (45), said armature being situated inside the tank (1) andseparated from the stator (4) by a magnetically permeable separationwall (43), said armature (44) forming a unit with an impeller (5) whichpushes water in the lower zone (1b) of the tank (1) radially outwardtoward the wall of the tank (1), forming a toroidal vortex (7,8) whosecenter region (7) draws hot water from the water body in the upper zone(1a) of the tank (1) downward, replacing said radially pushed coldwater, which is moving upward from the lower zone (1b) to said upperzone (1a).
 2. A fluid flow machine as per claim 1, characterized in thatthe motor (4) is switched on by a thermostat (52) as soon as thetemperature of the water surrounding the impeller (5) falls below apredetermined temperature.
 3. A fluid flow machine as per claim 1,characterized in that the motor (4) is mounted between two rings(46,51), of which the inner ring (46) is permanently fixed to the tankwall (3,31) and the outer ring (51) is held against a rim (52) of themotor (4) by means of bolts (47,50) distributed along the circumferenceof the ring (51).